1. Field of the Invention
This invention relates to means for attenuating the power of a laser beam in a laser-operated medical treatment device which is used, for instance, as a laser knife.
2. Background Art
A Co.sub.2 laser beam and an Nd-YAG laser beam are generally employed for a laser-operated medical treatment device which utilizes the thermal energy of a laser beam. In the case where an endoscope is used, an Nd-YAG laser is extensively employed because its beam is effectively transmitted through the flexible optical fiber transmitting the laser output. A contact type medical treatment has been put into practice in which a transparent sapphire member is attached to the end of the optical fiber receiving the beam from an Nd-YAG laser, and the diseased part is cut or congealed with the end of the sapphire member held in contact therewith.
In the contact type medical treatment, the transparent sapphire member is brought into direct contact with the diseased part as was described above, and therefore reflection and scattering of the laser beam at the diseased part are suppressed. Accordingly, in the contact type medical treatment, medical treatment can be carried out with low laser power and the effect is greater than with the same power in a non-contact type medical treatment. In the case of congealing the diseased part, the non-contact type medical treatment requires a laser power of more than 30 W, while in the contact type medical treatment the same effect can be obtained with a laser power which is about one-third (1/3) of this value.
On the other hand, in stopping bleeding, the Nd-YAG laser beam should have a high power of the order of 100 W. Accordingly, in order to use an Nd-YAG laser beam generator as a general-purpose laser beam generator, the Nd-YAG laser beam generator should be able to generate a laser beam in a range of from a low output of several watts to a high output of 100 W or higher.
However, it is impossible for a conventional 100 W Nd-YAG laser beam generator to stably provide a low output of the order to 10 W because, in the laser beam generator, the threshold value for population inversion for starting laser beam generation corresponds to an output of about 10 W. That is, if current control is carried out so that the intensity of the exciting lamp is changed for a low output, then the laser beam generated is considerably unstable. Therefore, heretofore, the above-described contact type medical treatment was required to use a special low-output Nd-YAG laser beam generator.